The overall objectives of the proposed work are to elucidate mechanisms operative in the control of parathyroid hormone biosynthesis, secretion and metabolism, and factors which influence the metabolism of vitamin D. The work in progress is primarily concerned with the control of parathyroid hormone secretion and metabolism. The possible role of a calcium binding protein present in parathyroid tissue in the regulation of parathyroid hormone production is being investigated. Specific studies include: (1) the effects of experimentally induced parathyroid hyperplasia on the concentration of the calcium binding protein in the parathyroid gland; (2) the effects of magnesium on the adenylate cyclase activity of parathyroid tissue; (3) the metabolism of PTH by liver membrane in vitro; and (4) the development of an assay for 1,25-dihydroxyvitamin D. BIBLIOGRAPHIC REFERENCE: 1-alpha-Hydroxyvitamin D3 in Chronic Renal Failure, J.C.M. Chan, S.B. Oldham, M.F. Holick and H.F. DeLuca. JAMA 234:47-52, 1975.